diff -up firefox-128.8.0/widget/gtk/nsWindow.cpp.kiosk-vsync firefox-128.8.0/widget/gtk/nsWindow.cpp
--- firefox-128.8.0/widget/gtk/nsWindow.cpp.kiosk-vsync	2025-03-13 13:04:03.112498669 +0100
+++ firefox-128.8.0/widget/gtk/nsWindow.cpp	2025-03-13 13:06:13.227823446 +0100
@@ -6348,9 +6348,13 @@ nsresult nsWindow::Create(nsIWidget* aPa
   // Initialize the window specific VsyncSource early in order to avoid races
   // with BrowserParent::UpdateVsyncParentVsyncDispatcher().
   // Only use for toplevel windows for now, see bug 1619246.
+  //
+  // Disable vsync for the kiosk mode - it cause the black screen
+  // This will be fixed in Firefox 140
   if (GdkIsWaylandDisplay() &&
       StaticPrefs::widget_wayland_vsync_enabled_AtStartup() &&
-      IsTopLevelWindowType()) {
+      IsTopLevelWindowType() && 
+      !gKioskMode ) {
     mWaylandVsyncSource = new WaylandVsyncSource(this);
     mWaylandVsyncDispatcher = new VsyncDispatcher(mWaylandVsyncSource);
     LOG_VSYNC("  created WaylandVsyncSource");